The degree of sophistication and complexity of low voltage (LV) distribution networks, also simply referred to as LV networks, has increased significantly over the past years which has been followed by increasing demands in terms of efficient use of energy, network protection and automation as well as to more stringent safety needs.
For instance, urban low voltage networks in the United Kingdom are supplied from MV/LV substations having a primary voltage of 11 kV and a secondary voltage of 240V. Substation transformers vary in size from 200 kVA to 1 MVA and the 3-phase LV network cables are connected to LV panels with each phase individually fused. Up to 15 network cables can be connected to an individual substation LV panel with 4 or 5 cables being typically connected. Each cable is protected by 3 individual 315 A, 400 A or 500 A J-type fuses and is connected to a number of LV link boxes which are connected in series. Individual customer's service connections are made to the LV network using branch joints onto the network cables between the link boxes.
If there is a fault on the LV network one or more fuses on the affected feeder will blow and clear the fault. Fault restoration involves sectionalising the affected LV network repeatedly by opening or removing wedge style links from the LV link boxes on the network and re-energising the circuit from the LV fuse panel.
However, since all these operations are at the present time still performed manually by a specialized team or technician displaced to the network location, customers may have to wait a number of hours before energy supply can be restored following a LV network fault.
Further, there are currently restrictions on the number of times a cable which has a fault can be energised to minimise risk of injury or further damage to other utilities plant which may be in contact with the faulted cable. In order to reduce the number of customer minutes lost and reduce the penalties imposed by the regulator, utilities have started to add remote control and automation to their MV network and are now examining the options for automation of the LV network.
For instance, published UK patent application GB 2 361 592 A describes a method and apparatus for controlling a portion of an electricity distribution network including conductors, a plurality of network devices cooperating with the conductors to facilitate distribution of electricity, and control apparatus co-located with selected network devices. A detection module for detecting fault conditions is also provided at each of the selected network devices. The distribution network state at each selected network device is monitored by the respective control apparatus and, upon detection of an abnormal condition in the distribution network, one of the control apparatus temporarily assumes coordinating control of the respective network portion. However, since each of the network devices has a dedicated control apparatus and respective detection module, this scheme is not suitable for current LV distribution networks having a high number of link boxes to be monitored and switches to be controlled.
U.S. Pat. No. 6,167,525 describes a method and system for analysing the status of an electric power transmission link and facing unexpected anomalous conditions in the transmission link during the operation of the link itself by timely redefining the thermal evaluation model to these unexpected conditions of the transmission link, in order to determine its instant load carrying capability. The method includes dividing the link into a predetermined number of segments, each segment having an associated prediction model and at least two associated temperature sensors. Upon receiving sensor values, an expected operating condition in one of the segments is determined based on the sensor value and the electric current value. Next, an actual operating condition in the segment is determined and compared with the expected operating condition. If there is a difference between the conditions, a second predetermined prediction model is associated with the segment. This technique is however insufficient for promptly responding to the occurrence of sudden fault events.